1. Field of the Invention
The present invention relates to a liquid crystal display device that uses OCB (Optically Compensated Bend) liquid crystal display elements in order to display an image.
2. Description of the Related Art
The liquid crystal display device includes a liquid crystal display panel that constitutes a matrix array of OCB liquid crystal display elements. The liquid crystal display panel includes an array substrate in which a plurality of pixel electrodes are covered with an alignment film and arrayed in a matrix, a counter-substrate in which a counter-electrode is covered with an alignment film and disposed so as to face the pixel electrodes, and a liquid crystal layer that is held between the array substrate and the counter-substrate in contact with each of the alignment films. Further, the liquid crystal display panel is configured such that a pair of polarizers are attached to the array substrate and the counter-substrate via optical retardation plates (see Jpn. Pat. Appln. KOKAI Publication No. 9-185032, for instance). Each of the OCB liquid crystal display elements serves as a pixel in a range of the associated pixel electrode. In the OCB liquid crystal display element, the alignment state of liquid crystal molecules needs to be transitioned from a splay alignment to a bend alignment, which is capable of displaying an image, with the application of a transition voltage that is different from a normal driving voltage.
For example, in TV sets and mobile phones, a liquid crystal display device is connected to an image information processing unit provided as an external signal source. A display and a sync signal are input from the image information processing unit to the liquid crystal display device, thereby enabling the liquid crystal display device to effect display. The image information processing unit includes a microcomputer that performs an image information process, and a power supply unit that outputs a power supply voltage to the microcomputer and the liquid crystal display device. As is illustrated in FIG. 7, a power switch is turned on at T1, and after the power supply unit is stabilized, the output of the power supply voltage begins at T2. The microcomputer starts the image information process at T3 after the elapse of a predetermined time from T2. A sync signal and a display signal, which are obtained at T4 as a result of the image information process, are delivered to the liquid crystal display device.
The liquid crystal display device is provided with a driving circuit for driving the OCB liquid crystal display elements. In the prior art, the driving circuit uses the sync signal from the image information processing unit also as a clock signal that is necessary for applying a transition voltage. Specifically, the application of the transition voltage is started at T4 at which the clock signal is supplied from the image information processing unit, and a time period during which the transition voltage is applied is measured with reference to the clock signal. If the transition to the bend alignment is completed at T5, the driving circuit drives the OCB liquid crystal display elements with use of the sync signal and display signal, thus causing the OCB liquid crystal display elements to display an image corresponding to the display signal. In this structure, a setup time (T1-T5) of two or three seconds is needed. Users of TV sets and mobile phones feel this setup time very long.